1. Field of the Invention
The present invention relates to an apparatus for the endless projection of a cinematographic film, comprising a rotatably journalled table for axially supporting a spiral-like film roll, a winding drum coaxially arranged on the table and having an annular support body for radially supporting the innermost winding of the film roll, first guide rollers for continuously delivering the film from the innermost winding of the film roll for the purpose of feeding the film to a film projector, and further guide rollers for guiding the film coming back from the film projector to the outermost winding of the film roll.
2. The Prior Art
Usually, a cinematographic film has a forward or leading end and a rear or trailing end. Generally, such a film is handled in form of a spiral-like film roll placed on a winding core or winding drum, one end of the film strip being releaseably fixed at the winding core or winding drum. In accordance with a widely practised method, the film strip is drawn off from the outer periphery of the film roll as it is projected, then passed through the projector, and thereafter re-wound on a second winding core or winding drum. By doing so, the leading end of the film strip comes to lie at the inner periphery of the second film roll being formed. To allow another projection of the film, it is necessary to rewind the film strip before it can be projected again.
In order to avoid the necessity of rewinding the film, apparatus have been constructed which allow the film to be continuously unwound from the inner periphery of a film roll as the film is projected, and to continuously rewind the film leaving the projector so that a second film roll is built up in which the leading end of the film again is the innermost end. The so formed second film roll is then immediately ready for a further projection of the film, whereby again the film is unwound from the inner periphery of the film roll. With this known apparatus the necessity for rewinding the film after each projection is eliminated. However it is still necessary to load the leading end portion of the film into the projector and to fix it at another winding drum for each further projection. Thus, an endless projection is not possible.
On the other hand, it is also known to connect the trailing end of a film with the leading end thereof so as to form an endless loop which can continuously be projected. In practice, however, serious problems do arise where the film is of considerable length. In a known apparatus for the endless projection of a film, a major portion of the film is guided in the form of a meander strip around a great number of guide rollers. Particularly for substandard films, apparatus have also become known in which the endless film is continuously rewound from the inner periphery of a spiral-like film roll and, after having passed through the projector, is continously wound up on the outer periphery of the same film roll. It is clear that with this method the consecutive or neighboured windings of the film roll travel with different angular speed, which consequently causes some friction between the neighboured windings when the inner and the outer diameters of the film roll are maintained at constant values. The technical problems thus caused increase with increasing gauge, length and weight of the film. The mentioned problems essentially occur in view of preserving a good condition of the film, i.e. in avoiding scratches and scrapes in the emulsion of the film due to friction of the windings of the film roll and in avoiding damage to the film perforations due to excessive high tension forces necessary for the continous feed or travel of the film.
In view of the before-mentioned technical problems, it is not surprising that satisfactory apparatus for the endless projection of longer cinematographic films of the standard 35 mm gauge, or larger, have not been available until now. It should be remembered that a commercial 35 mm motion-picture film of 90 minutes projection time has a length of 2,500 m and a weight of about 17 kg.
It is the main object of the present invention to provide an improved apparatus for the endless projection of cinematographic films which ensures an unattained careful handling of the film so that 35 mm and even larger motion-picture films having a projection time of more than 1 hour may be continuously projected.